diff --git a/lisp/init-nix.el b/lisp/init-nix.el
index 6f8d235def..d0f0671cec 100644
--- a/lisp/init-nix.el
+++ b/lisp/init-nix.el
@@ -2,12 +2,20 @@
 ;;; Commentary:
 ;;; Code:
 
-(when (or (maybe-require-package 'nix-ts-mode)
-          (maybe-require-package 'nix-mode))
-  (maybe-require-package 'nixpkgs-fmt)
+(if (maybe-require-package 'nix-ts-mode)
+    (progn
+      (defun sanityinc/set-nix-ts-auto-mode ()
+        (when (and (fboundp 'treesit-ready-p)
+                   (treesit-ready-p 'nix)
+                   (fboundp 'nix-ts-mode))
+          (add-to-list 'auto-mode-alist '("\\.nix\\'" . nix-ts-mode))))
+      (add-hook 'after-init-hook 'sanityinc/set-nix-ts-auto-mode))
+  (maybe-require-package 'nix-mode))
 
-  (with-eval-after-load 'eglot
-    (add-to-list 'eglot-server-programs '((nix-mode nix-ts-mode) . ("nil")))))
+(with-eval-after-load 'eglot
+  (add-to-list 'eglot-server-programs '((nix-mode nix-ts-mode) . ("nil"))))
+
+(maybe-require-package 'nixpkgs-fmt)
 
 (provide 'init-nix)
 ;;; init-nix.el ends here